1. Field of the Invention
The present invention relates to an actuator device comprising a rotation body having a rotation axis and drive means for changing the posture (position) of the rotation body and holding it at the changed position.
2. Description of the Related Art
In recent years, for the application to optical switch devices and the like in optical transmission systems such as an optical LAN in particular, an actuator device which can provide a high precision displacement at a high speed is desired. To apply such an actuator device to an optical switch, the device is required to have a moving velocity of ten and some m/s and a mirror positioning accuracy of about plus or minus 1 μm, and various methods have been proposed. Among those methods, since mechanical optical switches can directly change the propagation direction of light by mechanically driving a fiber or a mirror (or a shield plate), they have advantages in that the light loss and crosstalk inside a switch is smaller than those of optical switches of other methods, and are being put into practical uses as the most promising technique which can be applied to optical switches.
As the mechanical optical switch technology including an optical switch part and an actuator part, which is a prior art in that technical field, a mirror-drive mechanical 2×2 optical switch has been disclosed (see, for example, Japanese Patent Application Laid-Open No. 2001-75026 (FIG. 6 in pages 9 to 10)). Further, there is an actuator device which is applicable to mechanical optical switches as an example of other prior arts, which can be used as a 2×2 optical switch and in which the optical switch part has a common configuration and only the actuator part has a different configuration. This prior art will be described in detail referring to FIG. 11.
First, the optical fiber part 3 constituting an optical switch will be explained. This optical fiber part 3 comprises a first collimator lens assembly 105 in which a pair of optical fibers 101, 103 are placed in symmetry of the optical axis of the lens, and s second collimator lens assembly 111 in which a pair of optical fibers 107, 109 are placed, and the first and second collimator assemblies 105, 111 are oppositely placed to align the optical axes. In this configuration, the first and second collimator lens assemblies 105, 111 are supported in a manner such that the optical fiber 101 and the optical fiber 109, and the optical fiber 103 and the optical fiber 107 are optically connected crossing with each other.
Next, an actuator part 5 will be described. The actuator part 5 is placed in a housing 1 of any size, and the rotation axis 15 is rotatably supported by the rotation axis holding member 43 which are provided on the bottom face 41 of the housing 1 by being held between the pair of the rotation axis holding members 43 and the axis pressing spring 13 fixed to the housing 1. Moreover, the rotation axis 15 is held in the thrust direction with its one end abutting against the block 47 and with the other end being applied a fixed pressure by a thrust spring 49. There are fixedly inserted a rotor magnet 17 and a mount part 45 in the middle part of the rotation axis 15. These rotation axis 15, the rotor magnet 17 and the mount part 45 constitute a rotation body 7.
This actuator part 5 includes a first yoke 23 and a second yoke 27 which are made of a magnetic material such as electromagnetic soft iron. The first yoke 23 is magnetically coupled by combining a plurality of parts, and can self-hold the rotation body 7 at a first rotation position to be described later with a holding force which is a magnetic attraction force by which the rotor magnet 17 is attracted to the first yoke 23. In a like manner, the second yoke is magnetically coupled by combining a plurality of parts and can self-hold the rotation body 7 at a second rotation position to be described later with a holding force which is a magnetic attraction force by which the rotor magnet 17 is attracted to the second yoke 27.
The first yoke 23 is wound with a fist exciting coil 25 to form a fist magnetic circuit 9. This first magnetic circuit 9 moves the rotation body 7, which is in a self-holding state at the first rotation position, to the second rotation position by generating an enough rotational force to move the rotation body 7 from the first rotation position to the second rotation position to be described later.
The second yoke 27 is wound with a second exciting coil 29 to form a second magnetic circuit 11. This second magnetic circuit 11 moves the rotation body 7, which is in a self-holding state at the second position, to the first rotation position by generating an enough rotational force to move the rotation body 7 from the second rotation position to be described later to the first rotation position.
The first magnetic circuit part 9 and the second magnetic circuit part 11 are fixed to the housing 1 with screws (not shown) or the like. The terminal of the first exciting coil 25 and the terminal of the second exciting coil 29 are connected to a terminal pin (not shown) or FPC (flexible printed circuit) (not shown), and are taken out of the housing 1 to provide an electrical connection to the outside thereby controlling the actuator device.
Next, the rotation body 7 will be described referring to FIG. 12. The rotation body 7 is configured such that a rotor magnet (not shown) and a mount part 45 are fixed to the rotation axis 15 by means of adhesion or press fitting. The rotation body 7 is rotatably supported by a rotation axis holding member 43 provided on the bottom face 41 of the housing 1 by being held between the two rotation axis holding members 43 and the axis pressing spring (not shown) fixed to the housing 1. Moreover, a first rotation restriction part 57 and a second rotation restriction part 59 are provided on the bottom face 41 of the housing at a position spaced apart from the center of the rotation axis.
Next, the rotation restriction structure of the actuator part 5 will be described.
The state in which the rotation body 7 including the rotor magnet 17 is self-held at the first rotation position will be described referring to FIG. 13A. It is supposed here that the rotor magnet 17 is polarized into two poles in the direction shown in the figure. In FIG. 13A, reference numeral 21 denotes a reflection mirror surface provided in the rotation body 7 and reference numeral 35 denotes an optical path.
As shown in FIG. 13A, one end 31 of the first yoke 23 is located near the N pole of the rotor magnet 17, and the other end 33 is located near the S pole of the rotor magnet 17. The rotation axis 15 is rotatably supported by the rotation axis holding member 43 provided on the bottom face 41 of the housing 1, and is pressed down by an axis pressing spring 13 from above. Moreover, there is arranged a first rotation restriction part 57 on the bottom face of the housing 1 at a position which allows the contact with the first abutment part 53 of the mount part 45 constituting the rotation body 7.
Next, the magnetic circuit in a state in which the rotation body 7 is self-held at the first position will be described referring to FIG. 13B. The magnetic flux, which has been generated at the N pole of the rotor magnet 17, flows through the gap to one end 31 of the first yoke 23 which is the magnetic material located at a closest position, and flows through the first yoke 23 to the other end 33 of the first yoke 23, and further flows from the other end 33 of the first yoke 23 to the S pole of the rotor magnet 17 through the gap.
A closed magnetic circuit is formed by the flow of the magnetic flux as shown in FIG. 13B, and a magnetic attraction force is generated between the rotor magnet 17 and the first yoke 23, thereby the rotation body 7 being self-held at the first rotation position. The state in which the rotation body 7 is self-held at the first rotation position enables to hold a state in which the light on the optical path 35 passing through the optical fiber is reflected by the reflection mirror surface 21.
Next, the state in which the rotation body 7 is self-held in the second rotation position will be described referring to FIG. 14A.
One end 37 of the second yoke 27 is located near the rotor magnet 17, and the other end 39 is located near the S pole of the rotor magnet 17. Moreover, on the bottom face 41 of the housing 1, a second rotation restriction part 59 is arranged at a position which allows the contact with the second abutment part 55 of the mount part 45 constituting the rotational body 7.
Next, the magnetic circuit when the rotation body 7 is self-held at the second rotation position will be explained referring to FIG. 14B. The magnetic flux, which has been generated at the N pole of the rotor magnet 17, flows through the gap to one end 37 of the second yoke 27 which is the magnetic material located at a closest position, and flows through the second yoke 27 to the other end 39 of the second yoke 27, and further flows from the other end 39 of the second yoke 27 to the S pole of the rotor magnet 17 through the gap.
A closed magnetic circuit is formed by the flow of the magnetic flux as shown in FIG. 14B, and a magnetic attraction force is generated between the rotor magnet 17 and the second yoke 27, thereby the rotation body 7 being self-held at the second rotation position. The state in which the rotation body 7 is self-held at the second rotation position enables to hold a state in which the light on the optical path 35 passing through the optical fiber is allowed to pass through.
However, the above described prior art still has the following problem. That is, when the rotation body 7 is moved from the first rotation position to the second rotation position, or from the second rotation position to the first rotation position, and a collision occurs between the first rotation restriction part 57 and the first abutment part 53, or between the second rotation restriction part 59 and the second abutment part 55, the force acting on the rotation body 7 tends to urge the rotation axis 15 in the direction to be floated up from the rotation axis holding member 43.
Now, the force which acts on the rotation body 7 when the rotation body 7 has been moved from the first rotation position to the second rotation position will be described referring to FIG. 15A and FIG. 15B.
Provided that the rotor magnet 17 constituting the rotation body 7 is polarized into N and S poles as shown in FIG. 15A, a current is applied to the first exciting coil 25 to generate a magnetic flux φ to polarize the one end 31 of the first yoke 23 into a N pole thereby generating a repulsive force FN between the N pole of the rotor magnet 17 and the one end 31 of the first yoke 23, and also the other end 33 of the first yoke 23 is polarized into a S pole thereby generating a repulsive force FS between the S pole of the rotor magnet 17 and the other end 33 of the first yoke 23. These repulsive forces FN, FS will cause the rotation body 7 to rotate about the rotation axis 15 in the clockwise direction up to the second rotation position.
To secure the movement of the rotation body 7 from the first rotation position to the second rotation position, it is required to keep the first exciting coil 25 in an energized sate for a sufficiently long time. In this case, rotation of the rotation body 7 is restricted by the contact between the second abutment part 55 of the mount part 45 and the second rotation restriction part 59, and thereby the rotation body 7 is subjected to a moment pivoted at the contact part A. The acting moment in such a case will be described referring to FIG. 15B.
Letting the distance from the contact part A to the part on which a repulsive force FS acts be RS, and the distance from the contact part A to the part on which a repulsive force FN acts be RN, the torque T acting on the center of gravity of the rotation body 7 is given by the following equation with the clockwise direction being the plus direction as shown in FIG. 15B.T=FS×RS−FN×RN
And if FS=FN (=Fm), the following condition holds:T=Fm(RS−RN)>0Thus, since the rotation body 7 is subjected to a rotational moment in the clockwise direction at the contact part A acting as a supporting point, the rotation body 7 is exerted by a force to push up the axis pressing spring 13 (i.e., to be floated up from the rotation axis holding member 43).
Next, the force which acts on the rotation body 7 when it has been moved from the second rotation position to the first rotation position will be described referring to FIG. 16A and FIG. 16B.
A current is applied to the second exciting coil 29 to generate a magnetic flux φ to polarize the one end 37 of the second yoke 27 into a N pole thereby generating a repulsive force FN between the N pole of the rotor magnet 17 and the one end 37 of the second yoke 27, and also the other end 39 of the second yoke 27 is polarized into a S pole thereby generating a repulsive force FS between the S pole of the rotor magnet 17 and the other end 39 of the second yoke 27. These repulsive forces FN, FS will cause the rotation body 7 to rotate about the rotation axis 15 in the counter-clockwise direction up to the first rotation position.
The torque T acting at that time on the center of gravity of the rotation body 7 is given by the following equation with the counter-clockwise direction being plus direction as shown in FIG. 16B.T=FN×RN−FS×RS
And if F=FS (=Fm), the following condition holds:T=Fm(RN−RS)>0Thus, since the rotation body 7 is subjected to a rotational moment in the counter-clockwise direction at the contact part A acting as a supporting point, the rotation body 7 is exerted by a force to push up the axis pressing spring 13 (i.e., to be floated up from the rotation axis holding member 43).
As have been explained so far, in both cases in which the rotation body 7 moves from the second rotation position to the first rotation position, and from the first rotation position to the second rotation position, the rotation body 7 is exerted by a force to be floated up from the rotation axis holding member 43. Therefore, when the spring force of the axis pressing spring 13 is weak, the rotation axis 15 will be floated up and may be detached from the rotation axis holding member 43.
To avoid such a phenomenon, it is necessary to specify the spring force of the axis pressing spring to be strong enough to prevent the rotation axis 15 from being floated up. However, when the spring force of the axis pressing spring 13 is increased, the friction resistance of the slide parts between the rotation axis holding member 43 and the rotation axis 15 will be increased thereby requiring the application of a high voltage and therefore a large current to operate that. For this reason, it becomes difficult to achieve a low voltage drive and a low current consumption operation.
Moreover, since the friction resistance between the rotation axis holding member 43 and the rotation axis 15 becomes large, the amount of wear in the slide parts will inevitably increase thereby degrading the durability.
When a conventional actuator device is used for an optical switch, the slope of the rotation axis 15 will change due to the wear and that positional change will lead to a change in the inclination of the mirror surface. Thereby, the change in the amount of loss of light from its initial stage may increase thereby causing a problem in view of the reliability of the device.